Return success for -M '?' query option.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@3008 c046a42c-6fe2-441c-8c8c-71466251a162

vl.c

@@ -6705,7 +6705,7 @@ void help(void)
 #endif
            DEFAULT_GDBSTUB_PORT,
            "/tmp/qemu.log");
-    exit(1);
+    exit(strcmp(optarg, "?"));
 }
 
 #define HAS_ARG 0x0001